Pilot-Assisted DFT Window Timing/ Frequency Offset Synchronization and Subcarrier Recovery

Synchronization, which is composed of estimation and control, is one of the most important functionalities of the receiver. It must be first performed by the receiver when receiving information data. In an OFDM system, synchronization can be divided into three different parts—carrier frequency offset synchronization, DFT window timing synchronization, and subcarrier recovery. As shown in Section 4.8, anOFDM system is very sensitive to frequency offset, which may be introduced in the radio channel, so accurate frequency offset synchronization is essential. Especially for burst mode data transmission in wireless LAN applications, we must keep the overhead, namely, the number of pilot symbols required for the synchronization, as low as possible. DFT window timing synchronization corresponds to symbol timing synchronization in single carrier transmission. However, it is much more difficult, because there is always an ‘‘eye opening’’ in each single carrier modulated symbol, whereas there are many ‘‘zero crossings’’ in each OFDM symbol. Therefore, normal synchronization algorithms such as zero-forcing cannot be adopted. Furthermore, subcarrier recovery means simultaneous regeneration of reference signals at all subcarriers used.